What is your soil texture?

What soil texture is

Soil texture is the mix of three sizes of mineral particle: sand, silt and clay. The USDA draws the lines at 2.0 to 0.05 millimeters for sand, 0.05 to 0.002 millimeters for silt and 0.002 millimeters and finer for clay. Texture controls how fast water drains, how much a soil holds and how it works when wet or dry, so gardeners, builders and septic and drainage designers all ask for it. The classes below are the ones in the Soil Survey Manual (Agriculture Handbook 18, 2017, chapter 3), the reference the Natural Resources Conservation Service uses for soil surveys.

How the classes are defined

The manual defines each class in words as well as in the triangle, and this calculator applies those words exactly. Sand is more than 85% sand with silt plus 1.5 times clay under 15. Loamy sand has that sum at 15 or more and silt plus twice the clay under 30. Sandy loam needs silt plus twice the clay of 30 or more, plus either 7 to under 20% clay with more than 52% sand, or under 7% clay with under 50% silt. Loam is 7 to under 27% clay, 28 to under 50% silt and 52% or less sand. Silt loam is 50% or more silt with 12 to under 27% clay, or 50 to under 80% silt with under 12% clay; silt is 80% or more silt with under 12% clay. Sandy clay loam is 20 to under 35% clay, under 28% silt and more than 45% sand. Clay loam and silty clay loam both have 27 to under 40% clay and differ in sand: over 20 to 45% for clay loam, 20% or less for silty clay loam. Sandy clay is 35% clay or more with more than 45% sand; silty clay is 40% clay or more with 40% silt or more; clay is 40% clay or more with 45% sand or less and under 40% silt. The table under the answer repeats these rules and highlights yours.

Worked example

A soil test reports 70% sand, 20% silt and 10% clay. Silt plus 1.5 times clay is 35, so it is not sand; silt plus twice the clay is 40, so it is not loamy sand. Clay is between 7 and 20 and sand is over 52, so it is sandy loam. For a jar test, say the settled soil is 5.0 inches deep after 24 hours, the one-minute sand layer is 2.0 inches, the silt added after two more hours is 2.0 inches and the rest, 1.0 inch, is clay. That is 40% sand, 40% silt and 20% clay, so loam. If you marked heights from the bottom instead (2.0, 4.0 and 5.0), the calculator turns them into the same 40, 40 and 20 percent.

Limits of the jar test

• The settling times are a convention. Cornell marks sand at one minute, silt after two more hours and uses the 24-hour depth as the total. Clemson Extension waits 48 hours for the clay mark. The timing is not identical to the lab's size limits, so jar results can drift a few points either way.
• Organic matter and aggregates blur the layers. The triangle covers the mineral fine earth only (particles under 2 mm). Floating compost, or clumps that did not break apart, shift the percentages; shaking thoroughly, as both extensions advise, helps.
• Class edges are sharp. A jar reading within a point or two of a boundary can go either way; run the test twice and use the class that appears more often.
• Texture is not fertility or drainage by itself. Structure, compaction and organic matter change how a soil behaves. For anything with a cost, such as a septic field or a foundation, get a laboratory analysis or the county soil survey.

How do I find my soil texture from sand, silt and clay?

Use the USDA texture classes from the NRCS Soil Survey Manual. They sort soil into twelve classes by the percentages of sand (2.0 to 0.05 mm), silt (0.05 to 0.002 mm) and clay (0.002 mm and smaller), which must add up to 100. For example, 40% sand, 40% silt and 20% clay is loam, because loam is defined as 7 to under 27% clay, 28 to under 50% silt and 52% or less sand. Enter your numbers above, or two of the three, and the blank one is filled in as the remainder.

How does the jar test work?

Cornell Cooperative Extension's version: sift the soil, fill a straight-sided jar one third to one half with it, top up with water, add a tablespoon of powdered dishwashing detergent, shake for five minutes and let it settle for 24 hours. Mark the total depth of settled soil. Shake again and mark the sand layer after one minute, then the silt layer after a further two hours. The rest of the soil, still hazy or just settling, is the clay. Each layer's thickness divided by the total is its percentage. With 2.0, 2.0 and 1.0 inches of sand, silt and clay in a 5.0-inch total you get 40% sand, 40% silt and 20% clay, which is loam.

Should I wait 24 or 48 hours for the clay?

Extension services differ. Cornell lets the jar sit for at least 24 hours before marking the total depth, while Clemson Extension waits 48 hours before marking the clay layer. Fine clay can stay in suspension for a long time, so a longer wait usually gives a thicker clay layer and a more reliable total. Either way the jar test is an estimate; for decisions that cost money, send a sample to a lab for a particle-size analysis.

What do the class names mean in practice?

The names describe how the mineral particles are balanced, not how fertile the soil is. The University of Georgia's soil guide describes the feel: sandy soils are gritty and will not hold a ribbon, silty soils are smooth, and clay soils form long ribbons when squeezed. Texture also steers water. The University of Arkansas Extension notes that clay soils absorb water slowly but hold a lot of it, so they suit lower drip flow rates and less frequent cycles, while sandy soils drain fast. The calculator names the class; managing it is a separate question.

Why do two nearly identical soils land in different classes?

Classes have sharp edges. By the manual's definitions, 52% sand, 28% silt and 20% clay is loam, while 52.5% sand, 27.5% silt and 20% clay is sandy clay loam. A reading near a boundary can fall either way, and lab results themselves have measurement error, so treat a result within a point or two of an edge as either neighbor.

Does organic matter count in the triangle?

No. The Soil Survey Manual defines texture on the fine earth, the mineral particles smaller than 2 mm, after organic matter is removed in the lab. A dark garden soil full of compost is classed by its mineral part. In a jar, floating organic matter can make the clay layer look thicker than it is, which is one more reason to read jar results as approximate.

Sources: USDA Natural Resources Conservation Service, Soil Survey Manual, Agriculture Handbook No. 18 (March 2017), chapter 3, “Particle-Size Distribution” and “Definitions of Soil Texture Classes and Subclasses”, pp. 119 to 125; Cornell Cooperative Extension, “Soil Textural Analysis — The Jar Test”; Clemson Cooperative Extension, HGIC, “Soil Texture Analysis: The Jar Test”; University of Georgia, “A Simplified Guide to Soil Textural Classes”; University of Arkansas System Division of Agriculture, FSA6174 (2026). Next steps: raised bed soil calculator, rain garden size calculator (which uses soil type), drip irrigation calculator and topsoil calculator.